Several United States patents have issued to the applicant for drying coal in a fluidized bed reactor. These include U.S. Pat. No. 5,830,246 (“Process for processing coal”), U.S. Pat. No. 5,830,247(“Process for processing coal”), U.S. Pat. No. 5,858,035(“Process for processing coal”), U.S. Pat. No. 5,904,741(“Process for processing coal”), and U.S. Pat. No. 6,162,265(“Process for processing coal”). The entire disclosure of each of these United States patens is hereby incorporated by reference into this specification.
Applicant's U.S. Pat. No. 6,162,265 illustrative of these patents. It describes and claims “1. A process for preparing an irreversibly dried coal, comprising the steps of: (a) providing a first fluidized bed reactor comprised of a first fluidized bed with a fluidized bed density of from about 30 to about 50 pounds per cubic foot, wherein said first fluidized bed is maintained at a temperature of from about 480 to about 600 degrees Fahrenheit, (b) feeding to said first fluidized bed coal with a moisture content of from about 15 to about 30 percent and a particle size such that all of the coal particles in such coal are in the range of from 0 to 2 inches, (c) feeding to said first fluidized bed liquid phase water, inert gas, and air, and subjecting said coal in said first fluidized bed to a temperature of from about 480 to about 600 degrees Fahrenheit for from about 1 to about 5 minutes while simultaneously comminuting and dewatering said coal, wherein:(i) while said coal is subjected in said first fluidized bed to said temperature of from about 480 to about 600 degrees Fahrenheit, it is comminuted, thereby producing at least one coarse fraction and at least one fine fraction, (ii) at least a portion of said fine fraction is entrained to a cyclone, and (iii) At least a portion of said fine fraction entrained to said cyclone is removed from said cyclone and fed to a cooler in which the temperature of said fine fraction is reduced by at least about 300 degrees Fahrenheit, (d) passing said comminuted and dewatered coal to a second fluidized bed reactor comprised of a second fluidized bed with a fluidized bed density of from about 30 to about 50 pounds per cubic foot, wherein said second fluidized bed is at a temperature of from about 215 to about 250 degrees Fahrenheit, wherein water, inert gas, and from about 0.5 to about 3.0 weight percent of mineral oil with an initial boiling point of at least about 900 degrees Fahrenheit is also fed to said second fluidized bed, and (e) reducing the temperature of said comminuted and dewatered coal from said temperature of from about 480 to about 600 degrees Fahrenheit to said temperature of from about 215 to about 250 degrees Fahrenheit in less than about 120 seconds.”
The process described in U.S. Pat. No. 6,126,265 works well with reactors with a diameter of less than about 4 feet, which generally have an output of about 200 tons per day. With larger reactors, wherein the output(s) often exceed 1,000 tons per day, the process is often not as efficient. Without wishing to be bound to any particular theory, applicant believes that, as the size of the reactor increases, the gas velocity produced in the process increases geometrically, often to the point where the desired density of the fluidized bed used suffers. As the density of the fluidized bed declines, the efficiency of the drying process decreases.
It is an object of this invention to provide an improved process for drying coal that is efficient with larger fluidized bed reactors.